The ability of a power device to sustain high voltage depends primarily on the reverse breakdown voltage of the particular PN junctions in the device structure. All semiconductor devices are limited by size. When the wafer is cut into chips and packaged to make devices, the crystal lattice of the silicon wafer gets greatly damaged. For power devices, if the cut passes through the device structure that is subject to high voltage, lattice damages can cause a large leakage current, which reduces the breakdown voltage and long-term reliability of the device. In power devices, affected by the non-ideal surface of the PN junction or the termination of the PN junction, the reverse breakdown voltage of PN junction is also influenced by the breakdown phenomenon that the local area near the surface or at the bend of junction is occurred earlier than that of the parallel plane junction in the body. The junction termination is a special structure designed to reduce the local electric field, improve the surface breakdown voltage and reliability, and make the actual breakdown voltage of the device closer to the ideal value of the parallel plane junction. In the vertical conductive device, the junction termination is usually distributed in the vicinity of the active region of the device, and is an auxiliary structure of the PN junction in the active region for receiving external high voltage.
At present, the junction termination structure of the power semiconductor device fabricated by planar process is usually provided with some extended structures at the edge of the main junction (usually curved). These extended structures, such as field plate (FP), field limiting ring (FLR) and junction termination extension (JTE), variation of lateral doping (VLD) and resistive field plate (such as Semi-Insulating Polysilicon (SIPOS)), RESURF, actually play the role of widening the depletion region of the main junction, thereby reducing the electric field and ultimately increasing the breakdown voltage. To achieve high breakdown voltage, the extended structures must be long enough to ensure the full expansion of the main junction's depletion region. Therefore, in the high-voltage devices, the existing extended type termination structures occupy too much area, resulting in an increase in device costs.